The puzzling results for different density

The simulation is about 24keV neutron bombing hydrogen matter(only hydrogen element included),
in one event, only the first recoiling energy of proton by primary neutron was recorded, when hydrogen matter density was 0.001g/cm3, the result is:

this result seems reasonable.

but when changing the density to 0.1g/cm3, the result is:

How the density of matter affect the recoiling energy of nuclei?

_Geant4 Version:_11.01
_Operating System:_Ubuntu 20.04
_CMake Version:_3.16


Recoiling nucleus means it is a nuclear reaction product when a projectile strike to target nucleus.
picking your case
n (24 keV) + 1H → 2H*
Recoil Velocity of 2H (cm.ns) = 1.077e-1 with E* = 0.012 MeV

When you say

This is unclear to me. Since the reaction will be pure capture reaction and populates 2H at 0.012 MeV, this nuclei certainly will stop in the medium on the choice of density.

More denser the medium less is the range of the recoil.


@drvijayraj , the cross section of n(p,d) reaction is much more less than n(p,p)n elastic scattering, so the proton max energy is Ep=4mnmp/(mn+mp)**2, the value is approximately 24keV.

Ofcourse in elastic scattering the energy will be different. BTW FYI using Hauser-Feshbach statistical MC with 10000 events provides significant cross section for 2H ~ 2097 mb which is non-elastic scattering case i.e. fusion.
For more information on the recoil energy based on mass asymmetry you can go through DWBA elastic calculations to have differential cross sections and their corresponding energies.

Nevertheless, it is understandable range dependency on medium density.